Minimize the Explosion pic and open the helicopter crash pic, right click and “add as new Layer”;
If the explosion is not the right size, you have to go back to the explosion picture and resize it, and then copy and paste until it is the right size!
Move the explosion layer where you want it. Then using the layers option Pallet, drop the transparency down until you can see through the explosion.
Using the eraser tool, erase the explosion where it overlaps the walls and parts of the chopper blades. It helps to expand the picture 3 or 4 times it’s normal size and adjust the eraser tools size.